Pressure transducers are used in a wide variety of machines and systems to sense fluid pressure and applied forces at transducer locations. Pressure transducers generally convert a magnitude of the applied pressure to an electrical signal representing the magnitude. For example, previously known capacitive pressure sensors convert a magnitude of applied pressure to a magnitude of electrical capacitance.
Some previously known pressure sense elements that can be used in pressure transducer applications are based on a capacitive sensing technology. An example of such a sense element uses a pair of ceramic plates and electrodes separated by an air gap, which form a parallel plate capacitor on a rigid ceramic plate substrate. A deformable ceramic plate forms a diaphragm, which adjusts the distance between two electrodes across the gap. A nominal capacitance of the sense element and an amount of change in capacitance under application of pressure loading are characteristics of the sense element that are determined by several mechanical factors. These factors include the thickness of the diaphragm, the area of the diaphragm that is allowed to deform, the area of the electrodes, and the thickness of the air gap between the electrodes.
In certain applications, the air gap distance between electrodes of a sense element is in the order of micrometers. Sense elements that are manufactured with such a small gap thicknesses can have high defect rates due to contamination by conductive particles in the air gap that can provide a conductive path between the electrodes. The conductive particles are difficult to completely eliminate during manufacturing.
To reduce manufacturing defects due to conductive particle contamination in the air gap of a sense element, some previously known capacitive sense elements have included a glass layer over one of the electrodes for providing electrical insulation between the electrodes. However, because glass layer has a different dielectric constant than air in the gap, glass layer has the detrimental effect of altering the sense element characteristics such as the nominal capacitance and the amount of change in capacitance under application pressure loading. Moreover, by including a glass barrier over one of the electrodes, the amount of deflection that the deformable ceramic plate can achieve before contacting the glass barrier is limited. In previously known capacitive sense elements that include an extra glass layer over one of the electrodes, changes to the sensor's capacitive response characteristics are minimized or reduced by minimizing the thickness of the glass layer or increasing the thickness of the air gap.